Hepatocellular carcinoma (HCC) and colorectal carcinomas are leading causes of cancer death worldwide (Akriviadis et al., Br J Surg 85(10): 1319-31 (1998)). Although recent medical advances have made great progress in diagnosis and therapeutic strategies, a large number of patients with cancers are still diagnosed at advanced stages and their complete cures from the disease are matters of pressing concern. Recent advances in molecular studies have revealed that alteration of tumor suppressor genes and/or oncogenes are involved in carcinogenesis, however the precise mechanisms still remain to be elucidated.
Recent advances in molecular biology suggest that multi-step processes underlie hepatocarcinogenesis as they do the genesis and progression of colon tumors. These processes involve qualitative and quantitative alterations of various gene products. The β-catenin/Tcf signaling pathway has been reported to be involved in morphogenesis during development (Wodarz and Nusse, Annu Rev Cell Dev Biol 14: 59-88 (1998); Polakis, Genes Dev 14: 1837-51 (2000); Bienz and Clevers, Cell 103: 311-20 (2000)). Recent progress in cancer research has underscored the importance of the signaling pathway in the development of human tumors, whether arising in the colon, liver, prostate, stomach, brain, endometrium, or elsewhere (Bullions and Levine, Curr Opin Oncol 10: 81-7 (1998)). Adenomatous polyposis coli (APC), a tumor suppressor, interacts with β-catenin, Axin, conductin, and glycogen synthase kinase-3β (GSK-3β) and facilitates the degradation of β-catenin via the ubiquitin-proteosome system (Polakis, Genes Dev 14: 1837-51 (2000)). Most sporadic colorectal tumors accumulate β-catenin in the cytoplasm and/or nucleus due to either the inactivating mutations in APC, AXIN1 or AXIN2 (conductin), or to stabilizing oncogenic mutations in CTNNB1 (β-catenin), which results in constitutive activation of β-catenin/Tcf transcriptional complex (Polakis, Genes Dev 14: 1837-51 (2000); Korinek et al., Science 275: 1784-7 (1997)). Consequently the complex activates target genes such as c-myc, cyclin D1, matrilysin (MMP-1), c-jun, fra-1, urokinase-type plasminogen activator receptor (uPAR), connexin43, CD44, PPAR-∂, AF-17 and ENC-1 (He et al., Science 281: 1509-12 (1998); Shtutman et al., Proc Natl Acad Sci USA 96: 5522-7 (1999); Brabletz et al., Am J Pathol 155: 1033-1038 (1999); Crawford et al., Oncogene 18: 2883-91 (1999); Mann et al., Proc Natl Acad Sci USA 96: 1603-8 (1999); van der Heyden et al., J Cell Sci 111: 1741-9 (1998); Wielenga et al., Am J Pathol 154: 515-23 (1999); He et al., Cell 99: 335-45 (1999); Lin et al. Cancer Res 61: 6345-9 (2001); Fujita et al., Cancer Res 61: 7722-6 (2001)). However, the precise mechanism of tumorgenesis by activation of this pathway in colorectal cancer remains to be solved.
Another protein, stathmin is also known to be associated with a wide range of cancers (Hanash et al., J Biol Chem 263: 12813-5 (1988); Roos et al., Leukemia 7: 1538-46 (1993); Nylander et al., Histochem J 27: 155-60 (1995); Friedrich et al., Prostate 27: 102-9 (1995); Bieche et al., Br J Cancer 78: 701-9 (1998)). Stathmin (Sobel et al., J Biol Chem 264: 3765-72 (1989); Sobel et al., Trends Biol Sci 16: 301-5 (1991)) is a cytosolic phosphorprotein consisting of 148 amino acid residues (19 kD) that has also been referred to as p19, prosolin, Lap18, oncoprotein 18, metablastin, and Op 18. The expression of stathmin was revealed to be very high in various multipotential embryonic carcinoma cells and in multipotential cells of the inner cell mass of the mouse blastocyst (Doge et al., Differentiation 50:89-96 (1992)). Stathmin exists in cells under several non-phosphorylated and phosphorylated forms, the pattern of which is depending on the state of proliferation, differentiation, or activation of the cells in many biological systems (Sobel et al., Trends Biol Sci 16: 301-5 (1991)). Further, the microtuble depolymerizing activity of stathmin is known to be regulated by the changes in its phosphorylation level, and the microtuble depolymerizing activity of stathmin is reported to play a critical role in the regulation of the dynamic instability of microtubles during the different phases of the cell cycle (Marklund et al., EMBO J15: 5290-8 (1996); Horwitz et al., J Biol Chem 272: 8129-31 (1997)). Extensive phosphorylation of stathmin occurs during mitosis (Strahler et al., Biochem Biophy Res Commun 185: 197-203 (1992); Luo et al., J Biol Chem 269: 10312-8 (1994); Brattsand et al., Eur J Biochem 220:359-68 (1994)) and seems essential for the progression of the cell cycle. However, the precise mechanism of the phosphorylation of stathmin and its relation to canceration remains to be elucidated.
cDNA microarray technologies have enabled to obtain comprehensive profiles of gene expression in normal and malignant cells (Okabe et al., Cancer Res 61: 2129-37 (2001); Lin et al., Oncogene 21: 4120-8 (2002); Hasegawa et al., Cancer Res 62: 7012-7 (2002)). This approach enables to disclose the complex nature of cancer cells, and helps to understand the mechanism of carcinogenesis. Identification of genes that are deregulated in tumors can lead to more precise and accurate diagnosis of individual cancers, and to develop novel therapeutic targets (Bienz and Clevers, Cell 103:311-20 (2000)). To disclose mechanisms underlying tumors from a genome-wide point of view, and discover target molecules for diagnosis and development of novel therapeutic drugs, the present inventors have been analyzing the expression profiles of tumor cells using a cDNA microarray of 23040 genes (Okabe et al., Cancer Res 61: 2129-37 (2001); Kitahara et al., Cancer Res 61: 3544-9 (2001); Lin et al., Oncogene 21: 4120-8 (2002); Hasegawa et al., Cancer Res 62: 7012-7 (2002)).
Studies designed to reveal mechanisms of carcinogenesis have already facilitated identification of molecular targets for anti-tumor agents. For example, inhibitors of farnexyltransferase (FTIs) which were originally developed to inhibit the growth-signaling pathway related to Ras, whose activation depends on posttranslational farnesylation, has been effective in treating Ras-dependent tumors in animal models (He et al., Cell 99: 335-45 (1999)). Clinical trials on human using a combination of anti-cancer drugs and anti-HER2 monoclonal antibody, trastuzumab, have been conducted to antagonize the proto-oncogene receptor HER2/neu; and have been achieving improved clinical response and overall survival of breast-cancer patients (Lin et al., Cancer Res 61: 6345-9 (2001)). A tyrosine kinase inhibitor, STI-571, which selectively inactivates bcr-abl fusion proteins, has been developed to treat chronic myelogenous leukemias wherein constitutive activation of bcr-abl tyrosine kinase plays a crucial role in the transformation of leukocytes. Agents of these kinds are designed to suppress oncogenic activity of specific gene products (Fujita et al., Cancer Res 61: 7722-6 (2001)).